Sibutramine (N-[1-[1-(4-chlorophenyl)cyclobutyl]-3-methylbutyl]-N,N-dimethylamine), which is a inhibitor of 5-hydroxytryptamine and noradrenaline reuptake in vivo (Neuropharmacology, 28, p 129-134), is useful in the treatment of depression, Parkinson's disease, obesity, insulin-independent diabetes mellitus, epilepsy, and the like. In addition, sibutramine reduces body weight gain by a dual action to reduce food intake by enhancing satiety and to increase energy expenditure by stimulating heat generation (Int. J. Obesity, 19, p 145; Brit. J. Pharmacol. 114, p 388). The therapeutic use of sibutramine in depression is described in British Patent Specification 2098602. The therapeutic use of sibutramine in Parkinson's disease is disclosed in International Pat. Publication No. WO88/06444. The therapeutic use of sibutramine in cerebral function disorders is disclosed in U.S. Pat. No. 4,939,175. The use of sibutramine hydrochloride in the treatment of obesity is disclosed in European Pat. No. 397831. Also, International Pat. Publication No. WO95/20949 discloses the use of sibutramine for improving impaired glucose tolerance or glucose tolerance in patients suffering from insulin-independent diabetes mellitus.
Typically, the preparation of salts having pharmaceutically useful physical properties must satisfy the following physicochemical criteria: (1) good solubility, (2) good stability, (3) good non-hygroscopicity and (4) compressibility into tablet form.
However, Korean Pat. Publication No. 94-8913 states that sibutramine hydrochloride has been known to contain a variable amount of water and thus be hygroscopic, and that non-hygroscopic sibutramine can be obtained by preparing sibutramine hydrochloride in a monohydrate form. Sibutramine hydrochloride monohydrate has been prepared by brining it into contact with a medium consisting of water or a medium containing water. Since sibutramine is difficult to purify due to its low melting point, it is preferable to use a crystalline material capable of being purified by recrystallization in order to prepare a pharmaceutical composition comprising sibutramine. Korean Pat. Publication No. 1990-0000274 discloses that sibutramine is utilized as salts formed with acids providing non-toxic acid addition salts containing pharmaceutically acceptable anions, for example, in the form of hydrochloride, malate, acetate, citrate, fumarate, tartrate, succinate, aspartate or glutmate salt.
However, since sibutramine hydrochloride is difficult to handle pharmaceutically due to its hygroscopic nature, it is undesirable to use sibutramine hydrochloride for preparing medicaments. In the preparation of medicaments, a constant weight of an active compound should be contained in each dosage form, but an active ingredient absorbing water from the surrounding environment makes it difficult to achieve such consistency. Korean Pat. Publication No. 94-8913 discloses that when sibutramine hydrochloride is prepared in a monohydrate form, a non-hygroscopic product is obtained, which is suitable for the preparation of capsules, tablets and other pharmaceutical dosage forms. This patent publication describes that sibutramine hydrochloride monohydrate can be prepared by contacting sibutramine hydrochloride with a medium consisting of or containing water, which is a water-immiscible solvent or a water-miscible solvent.
The currently used sibutramine hydrochloride monohydrate is prepared by a complicated process including adding a predetermined amount of water to a reaction mixture, or including preparing sibutramine hydrochloride anhydrate and suspending the sibutramine hydrochloride anhydrate in a water-containing solvent for a long time with agitation. In addition, since sibutramine hydrochloride monohydrate has relatively low solubility between pH 1.0 and pH 7.4, substitute salts having better solubility need to be developed in order to improve the bioavailability of sibutramine.
In this regard, intensive and through research into the development of novel salts of sibutramine, capable of solving the problems encountered in the prior art, conducted by the present inventors, resulted in the finding that among dicarboxylic acid salts of sibutramine, sibutramine oxalate and sibutramine malonate in anhydrous forms, which do not require a complicated process for preparing a hydrate, possess remarkably high solubility in water, and also exhibit non-hygroscopicity and stability.